1. Field of the Invention
The present invention pertains to novel coordination polymerization catalysts having utility for the polymerization and copolymerization of ethylene and alpha olefins and optionally diene monomers. More specifically the invention relates to hydrocarbon soluble Ziegler catalysts that contain bidentate ligands on transition metal compounds such as those based on vanadium.
2. Description of Related Art
Ethylene-alpha-olefin copolymers, particularly elastomers, are important commercial products. Of these, copolymers of ethylene and propylene are especially important. Two basic types of ethylene-propylene copolymers are commercially available. Ethylene-propylene copolymers (EPM) are saturated compounds requiring vulcanization with free radical generators such as organic peroxides. Ethylene-alpha-olefin terpolymers (e.g., EPDM) contain a small amount of non-conjugated diolefin, such as dicyclopentadiene, 1,4-hexadiene or 5-ethylidene-2-norbornene (ENB), which provides sufficient unsaturation to permit vulcanization with curing agents other than peroxides, such as sulfur. Such polymers that include at least two monomers, e.g., EPM and EPDM, will hereinafter be collectively referred to as ethylene-based copolymers.
These copolymers have outstanding resistance to weathering, good heat aging properties and the ability to be compounded with large quantities of fillers and plasticizers resulting in low cost compounds which are particularly useful in automotive and industrial mechanical goods applications. Typical automotive uses are tire sidewalls, inner tubes, radiator and heater hose, vacuum tubing, weather stripping and sponge doorseals and Viscosity Index improvers for lubricating oil compositions. Typical mechanical goods uses are for appliance, industrial and garden hoses, both molded and extruded sponge parts, gaskets and seals and conveyor belt covers. These copolymers also find use in adhesives, appliance parts as in hoses and gaskets, wires and cable and plastics blending.
The properties of these ethylene-based copolymers are a function of the catalyst system and polymerization process used to produce them. Elastomeric olefin copolymers may be produced at relatively low polymerization temperatures and pressures by means of the so called Ziegler - Natta catalysts which comprise a transition metal compound used in combination with a metal alkyl. More specifically, certain catalyst systems based on a combination of a vanadium compound, an aluminum alkyl or aluminum alkyl halide and, in some cases, a halogen-containing organic compound which serves as a polymerization promoter are known in the art.
For example, U.S. Pat. No. 4,540,753 relates to ethylene copolymers with narrow molecular weight distribution (MWD) and a narrow inter molecular compositional distribution (CD). The catalyst system used in this reference may comprise VCl.sub.4, or pentavalent or trivalent hydrocarbon-soluble vanadium compound having the formula: ##STR1## where x is O-3 and R is a hydrocarbon radical, and an organo-aluminum compound. In the polymerization process, the catalyst components are premixed in the premixing device and aged for 1-50 seconds.
U.S. Pat. No. 4,508,842 discloses gas phase homo or copolymerization of ethylene using a supported catalysts made by treating VCl.sub.3 with a Lewis base. The Lewis bases taught in the patent are not chelating agents, but rather monodentate ligands.
U.S. Pat. No. 4,066,571 discloses that polymerization catalysts can be made by treating transition metal salts with acetylating agents. In example 7 therein, the salt acetylated is VCl.sub.3. Vanadium compounds are also used in Examples 15 and 33 thereof.
Though not directed to coordination polymerization or to catalyst compounds useful therein, Cotton et al. Inorg. Chem. 25 3505-3512 (1986) discloses certain vanadium carboxylates and utilizes acetic acid in preparing the same. No utility is taught for the resulting product. Additionally, since the Cotton et al, product will be largely insoluble in hydrocarbon solvents, it would not appear to have utility in Ziegler solution polymerization where hydrocarbon soluble catalysts are required.
In the area of ethylene and alpha olefin polymerization, a need has existed for the development of new hydrocarbon soluble Ziegler polymerization systems which have the capability of polymerizing at higher temperatures in continuous flow stirred tank reactor (CFSTR) polymerization reactions than those used with traditional catalyst such as VCl.sub.4, without having the catalyst efficiency decrease as significantly as at temperatures above 40.degree. C. A further need has existed to provide a vanadium catalyst that produces more polymer i.e., has greater catalyst efficiency, under identical conditions than a conventional vanadium based catalyst such as VCl.sub.4.
A further need has existed for a vanadium catalyst system that is more efficient in converting more of the vanadium into active catalyst than the heretofore described prior art VCl.sub.4 catalyst. For example, with respect to tubular reactor systems such as disclosed in U.S. Pat. No. 4,540,753, use of catalyst systems containing vanadium compounds such as VCl.sub.4 has shown that the requisite pre-mixing and aging of catalyst components has resulted in significant deactivation of some portion of the catalysts formed. In some cases deactivation has occurred in up to 55 mole percent of catalyst formed based on the moles of the initial vanadium compound added. Reduction in the active catalyst is characterized by consequent reduction in polymerization efficiency.
A yet further need has been the desire to find a vanadium catalyst with an expanded lifetime beyond that which is currently obtained using VCl.sub.4 systems.